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E.E. Joslin et al. / Journal of Organometallic Chemistry xxx (2017) 1e5
4.2. Representative catalytic ethylene hydrophenylation reaction
TpRu(CO)(NCMe)Ph (0.0103 g, 0.0224 mmol, 0.1 mol % Ru rela-
tive to benzene) was dissolved in 2 mL of benzene. In a 25 mL
volumetric flask, n-decane (0.199 g, 0.273 mL, 0.5 mol % n-decane
relative to benzene) was added to benzene to produce a stock so-
lution containing an internal standard. To generate 6 mL of a
0.025 mol % Ru catalyst solution: 1.5 mL of a 0.1 mol % Ru solution,
1.5 mL of a 0.5 mol % n-decane solution and 3 mL of benzene were
transferred to a stainless steel pressure reactor. The reactor was
charged with 0.1 MPa of ethylene, pressurized with dinitrogen to a
total pressure of 0.8 MPa, and heated to 90 ꢁC. After a given dura-
tion of time the reactor was cooled to room temperature and an
aliquot of the reaction mixture was removed. The reaction mixture
was analyzed by GC/MS using peak areas of the products and the
internal standard to calculate product yields. Ethylbenzene pro-
duction was quantified using linear regression analysis of gas
chromatograms of standard samples. A set of eight known stan-
dards were prepared consisting of 1:5, 3:5, 5:5, 7.5:5, 10:5, 50:5,
100:5 and 150:5 M ratios of ethylbenzene to n-decane in methylene
chloride. A plot of peak area ratios versus molar ratios gave a
regression line. For the GC/MS system, the slope and correlation
coefficient for ethylbenzene were 0.18 and 0.99, respectively. All
reactions were repeated in triplicate to ensure reproducibility.
Fig. 3. Second-order plot for the decomposition of TpRu(CO)(NCMe)Ph in THF-d8 at
75 ꢁC, as monitored by 1H NMR spectroscopy (R2 ¼ 0.98).
3. Conclusions
TpRu(CO)(NCMe)Ph is an effective catalyst for ethylene hydro-
phenylation. In an effort to better understand possible pathways for
catalyst deactivation, the influence of catalyst loading and ethylene
pressure on catalytic performance and deactivation product was
examined. Based on these studies, there are two competing deac-
tivation pathways for catalytic ethylene hydrophenylation: 1) a
likely bimolecular decomposition pathway that results in the for-
mation of uncharacterized paramagnetic species, and 2) formation
4.3. Quantification of TpRu(CO)(h
3-C4H7) from catalytic
experiments
A catalytic reaction was performed as stated above. After
completion of catalysis, the reactor was brought into the glovebox,
and the volatiles were removed in vacuo. The non-volatiles were
dissolved in C6D6 (0.4 mL) and placed in an NMR tube with 20 mL of
a 5.0 mM HMDS (hexamethyldisiloxane) stock solution in C6D6. A
of the
h h
3-allyl complex TpRu(CO)( 3-C4H7), which arises due to
1H NMR spectrum was collected (pulse delay of 20 s) and an allyl
ethylene CꢀH activation (Scheme 2). It was determined that both
the starting catalyst precursor and ethylene concentration influ-
ence catalyst longevity as well as the dominant pathway for deac-
tivation. Higher catalyst loading and low ethylene concentrations
bias the decomposition toward the formation of paramagnetic
species, while low catalyst loading and high ethylene concentra-
resonance corresponding to TpRu(CO)(
tegrated relative to the HMDS standard to calculate the percent
yield of TpRu(CO)(
3-C4H7).
h
3-C4H7) (4.4 ppm) was in-
h
4.4. Kinetic measurements of TpRu(CO)(NCMe)Ph decomposition
THF-d8 solution of TpRu(CO)(NCMe)Ph (0.0125 g,
tions result in formation of TpRu(CO)(h
3-C4H7). Optimal catalytic
conditions for maximum turnovers were found to be with low
catalyst loadings and ethylene concentrations.
A
0.0272 mmol) and hexamethyldisilane (as an internal standard)
was made in a 1 mL volumetric flask. The solution was divided
(300 mL aliquots) and transferred into three J. Young NMR tubes.
The NMR tubes were placed into the temperature calibrated NMR
probe (equilibrated at 76 ꢁC). The temperature was determined
using a 80% Ethylene Glycol in DMSO-d6 and the following equation
provided by Bruker Instruments, Inc. VT-Calibration Manual: T(K) ¼
4. Materials and methods
4.1. General methods
(4.218e D)/0.009132, where D is the shift difference (ppm) between
Unless otherwise noted, all synthetic procedures were per-
formed under anaerobic conditions in a nitrogen-filled glovebox or
by using standard Schlenk techniques. Glovebox purity was main-
tained by periodic nitrogen purges and was monitored by an oxy-
gen analyzer [O2(g) < 15 ppm for all reactions]. The preparation,
isolation and characterization of TpRu(CO)Ph(NCMe) [31] and
CH2 and OH peaks of the ethylene glycol. Reaction progress was
monitored by 1H NMR spectroscopy using automated data acqui-
sition. A single transient was used for each time point with 900 s
delay between transients. The rate of the reaction was determined
by monitoring the disappearance of the most upfield Tp resonance
(6.02 ppm) of the starting material. The rate of decomposition was
determined utilizing data up to 75% conversion (30,000 s), as the
presence of a significant concentration of the resultant para-
magnetic product introduced substantial error in the resonance
integrations.
TpRu(CO)(h
3-C4H7) [29] have been previously reported. Benzene
was purified by passage through a column of activated alumina.
Benzene-d6 and THF-d8 were stored under a nitrogen atmosphere
over 4 Å molecular sieves. 1H NMR spectra were recorded on a
Varian MRS 600 MHz spectrometer. All 1H spectra are referenced
against residual proton signals. GC/MS was performed using a
Shimadzu GCMS-QP2010 Plus system with simulated electron
impact or electron impact ionization. Ethylene (99.5%) was pur-
chased from GTS-Welco and used as received. All other reagents
were used as received from commercial sources.
Funding
We thank the U.S. Department of Energy, Office of Basic Energy
Sciences, Division of Chemical Sciences, Geosciences, and Bio-
sciences for support of this research via grants DE-SC0000776
j.jorganchem.2017.03.051